Skipjack 20 rusted motor mount bolts

sprince

Newbie
May 6, 2020
24
16
62
agoura hills
Name
Stewart Prince
Boat Name
1972 Skipjack 20
The pain continues, after finding water between the inner liner and the hull in my 1972 Skipjack 20 open, I looked everywhere but could not find the source of the water. But it was fresh water. I thought it might be coming from the fish hold, but no. I ended up pulling the gas tank so I could see everything, now I could get under the engine and look for any kind of hole or crack, this is what I discovered:

The motor mount bolts had rusted out, not completely but one was loose letting water go from the bilge to the hull through the hole in the stringer. Quite a bit of water in fact. And of course the hole had some rot.

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After reading other posts on this topic and after freaking out I pulled the motor, now I could see the entire problem. These motor mounts are just screwed into the stringers using steel lag bolts, not stainless bolts. In fact, all the bolts on all 4 mounts were rusted somewhat. But the one by the transom was pretty bad. Not even any silicone! Maybe they didn't make it in 1972 when they made my boat.

So here is how I solved the problem, I'm only posting to possibly help someone else with the same problem. I had to drill a bunch of exploratory holes, both vertically and horizontally in the stringers to find the extent of the rot. The rot was only in one motor mount but in 2 holes. So I let the whole thing dry out for a month, then drilled 1/2 holes in the rotted sections and poured epoxy in. I did some quick calculations, turns out the thrust force on the prop can be over 2000 lbs at 150 hp. This also means the front motor mounts are being pushed up and the rear down. So I came up with a system of 5 vertical and 6 horizontal lag bolts to hold each motor mount, and I fabricated some "tee" style mounts out of aluminum plate.

Then I used two tubes of 3M 5200 to hold everything in place and I installed the mounts, they are shown below. Yes it is overkill and yes I spent too much pulling the motor, making the mounts etc but now I have piece of mind, at least when it comes to this (one of many) problem.



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sprince

Newbie
May 6, 2020
24
16
62
agoura hills
Name
Stewart Prince
Boat Name
1972 Skipjack 20
This is a better view of the exploratory holes I drilled while trying to find rot in the stringers. After removing the engine I made a template that had both vertical and horizontal holes drilled in it, I used it to drill the explore holes in the stringers. I did find some wet spots, not sure if it was rot, this is why I let everything dry for a month. The bad spots were overdrilled and filled with liquid epoxy. The picture shows the vertical holes, but there are horizontal ones as well. Then I made the TEE motor mounts from plate. Previous mounts were just L style, there were washers under the engine mounts to raise and lower the heights for positioning, very random, I used an old OMC raw engine block for positioning.

I tried my best to figure out the angle of the engine and stern drive, somewhere between 1/4 and 1/2 inch of tilt front to back, so I shimmed the back mounts 1/4 inch to start with, could not find any info on original trim angle. If the boat is not trimmed correctly I guess I'll add more spacers to the rear mounts.
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Farpoint

Member
Sep 18, 2019
349
418
Nanoose Bay, BC
Name
FarPoint
Boat Name
28 Skipjack, 733 Zodiac Hurricane
Is that an OMC stringer drive leg?
If so, just as an FYI, there was a trim system for that setup.
A bit weird, generally some available on EBay